Typically, electrophotographic page printers use a dry toner powder to develop a desired image on a photoconductive drum within the printer. This dry toner powder is contained in an assembly known as a toner print cartridge. The toner print cartridge is designed to operate in a given printer having sensors or mechanical switches therein which allow the internal software of the printer to determine if the toner cartridge has been properly installed before printing. This toner cartridge sensing scheme has been normally dedicated to only sensing the presence of the toner cartridge, but not the type of toner within the cartridge. A molded plastic tab has been typically employed on the toner cartridge as a means for depressing a cartridge sensing switch within the printer which thereby operates to indicate to the user and the printer the presence of a toner cartridge loaded therein. The print engine of the printer, the control software thereof, and the toner cartridge combination are difficult to modify in order to allow sensing of other desired features such as the use of a magnetic ink character recognition (MICR) toner, color toner, or other types of toner.
Another kind of cartridge-type identification system which is somewhat similar to the above plastic tab approach utilizes a projection member or unit in combination with a plurality of microswitches, all of which are located within the printer housing. The projection unit must be specifically located and positioned directly adjacent to a specifically selected microswitch so that the closure of this microswitch by the projection unit would indicate the particular type of print cartridge that has been loaded into the printer. This type of print cartridge identification system is described in U.S. Pat. No. 4,500,195 issued to Houoso and assigned to Canon of Japan, and is incorporated herein by reference.
There is yet another cartridge identification system which has been designed to detect the type of toner cartridge in addition to detecting the presence or absence of such cartridge in an electrophotographic printer. This system is described in U.S. Pat. No. 4,963,939 issued to Kurando et al, assigned to Mita Industrial Company of Japan and is also incorporated herein by reference. However, the Kurando et al system described in U.S. Pat. No. 4,963,939 employs a magnetic detection circuit in order to detect the permeability of the toner material within the print cartridge in order to identify the type of cartridge loaded therein. This magnetic detection circuit in Kurando et al utilizes sensors located on the outside of the print cartridge and employs magnetic coupling between these sensors located on the outside of the cartridge and the toner within the cartridge in order to generate the permeability-dependent output signals. This detection scheme not only requires relatively sensitive magnetic tuning circuitry and complex and costly output circuitry for driving output sensors, but in addition, and as a result of the use of the above magnetic detection circuit, the above Kurando et al system is not easily retrofittable into existing pinters. This magnetic coupling scheme would therefore require extensive modification to existing printer hardware in order to accomplish a retrofitting operation on existing printers.